A Novel Principle to Localize Scattered-wave Sensitivity Using Wave Interference and Its Adjoint

When using scattered waves for high-resolution imaging of a medium, the sensitivity of these waves to the spatiotemporal distribution of heterogeneities is undoubtedly a key factor. The traditional principle behind using scattered waves to detect small changes suffers from an inherent limitation when other structures, not of interest, are present along the wave propagation path. We propose a novel principle that leads to enhanced localization of wave sensitivity, without having to know the intermediate structures. This new principle emerges from a boundary integral representation which utilizes wave interferences observed at multiple points. When tested on geophysical acoustic wave data, this new principle leads to much better sensitivity localization and detection of small changes in seismic velocities, which were otherwise impossible. Overcoming the insensitivity to a target area, it offers new possibilities for imaging and monitoring small changes in properties, which is critical in a wide range of disciplines and scales.